Spacecraft induced error sources

The attitude control and measurement systems aboard the LANDSAT 2 and D satellites are described and associated errors are discussed. Also, the ephemeris errors from various tracking systems are examined. Use of the Global Positioning System and improved attitude control instruments is expected to greatly reduce the errors in LANDSAT D in comparison with previous LANDSATS

A precise description of the p-adic valuation of the number of alternating sign matrices

Following Sun and Moll, we study v_p(T(N)), the p-adic valuation of the counting function of the alternating sign matrices. We find an exact analytic expression for it that exhibits the fluctuating behaviour, by means of Fourier coefficients. The method is the Mellin-Perron technique, which is familiar in the analysis of the sum-of-digits function and related quantities

Fracturas de implantes de tibia. Consecuencias para los ensayos de los implantes

El objetivo de este trabajo es estudiar los modelos de fracturas de prótesis de tibia descritos en la literatura y, sobre la base de dichos conocimientos, desarrollar un ensayo para implantes en la cual se logren simular condiciones fisiológicas. El caso descrito con mayor frecuencia en la literatura es la migración de la parte medial de la prótesis, fenómeno que, a menudo, antecede a la fractura de la prótesis. La posición defectuosa resultante de dicha migración modifica el eje mecánico y provoca una sobrecarga en la parte medial de la prótesis. Se ha desarrollado un ensayo de implantes que simula el modelo de fallo in-vivo. Dos bases de material sintético de diferente dureza simulan la diferente densidad ósea medial y lateral, para permitir una migración del lado medial del platillo. En el ensayo dinámico el platillo tibial es sometido a una carga de un solo lado y el vástago de la prótesis se apuntala con un contrasoporte. Para simular el entorno fisiológico, todo el dispositivo se encuentra sumergido en una solución de Ringer a 37°. El implante de tibia es expuesto durante 10 millones de ciclos a una carga que corresponde al quíntuple del peso del cuerpo (4.000 N). El punto de aplicación de la fuerza fue tomado de datos de análisis del caminar (marcha en superficie plana, ascendente y descendente, subir escaleras). Con esta carga fisiológica se efectuaron los primeros ensayos. En éstas quedó demostrado que productos clínicamente exitosos podían superar el ensayo. Por el contrario, los productos con modelos de fracturas conocidos no la superaron. Los primeros resultados con estos productos demostraron también que el ensayo generaba muestras de fractura semejantes a las que se producen in vivo. Debido a la configuración fisiológica del dispositivo se somete el sistema completo es decir el platillo, el vástago de la prótesis y la unión - generalmente modular - entre ambos a ensayo. El "ensayo fisiológico de tibia " descrito ayuda a evaluar los diseños de tibia antes de que se autorice su venta. Nuevos implantes y modificaciones de diseño en implantes ya existentes son puestos a la venta después de cumplir con las exigencias del ensayo.Peer Reviewe

Bacterial protein microarrays for identification of new potential diagnostic markers for Neisseria meningitidis infections

Neisseria meningitidis is the most common cause of meningitis and causes epidemic outbreaks. One trait of N. meningitidis, which is associated with most of the currently recognized virulence determinants, is the presence of phase-variable genes that are suspected to enhance its ability to cause an invasive disease. To detect the immune responses to phase-variable expressed proteins, we applied protein microarray technology for the screening of meningitis patient sera. We amplified all 102 known phase-variable genes from N. meningitidis serogroup B strain MC58 by polymerase chain reaction and subcloned them for expression in Escherichia coli. With this approach, we were able to express and purify 67 recombinant proteins representing 66% of the annotated genes. These were spotted robotically onto coated glass slides to generate protein microarrays, which were screened using 20 sera of patients suffering from meningitis, as well as healthy controls. From these screening experiments, 47 proteins emerged as immunogenic, exhibiting a variable degree of seroreactivity with some of the patient sera. Nine proteins elicited an immune response in more than three patients, with one of them, the phase-variable opacity protein OpaV (NMB0442), showing responses in 11 patient sera. This is the first time that protein microarray technology has been applied for the investigation of genetic phase variation in pathogens. The identification of disease-specific proteins is a significant target in biomedical research, as such proteins may have medical, diagnostic, and commercial potential as disease markers

Trees with Given Stability Number and Minimum Number of Stable Sets

We study the structure of trees minimizing their number of stable sets for given order $n$ and stability number $\alpha$. Our main result is that the edges of a non-trivial extremal tree can be partitioned into $n-\alpha$ stars, each of size $\lceil \frac{n-1}{n-\alpha} \rceil$ or $\lfloor \frac{n-1}{n-\alpha}\rfloor$, so that every vertex is included in at most two distinct stars, and the centers of these stars form a stable set of the tree.Comment: v2: Referees' comments incorporate

Tur\'an Graphs, Stability Number, and Fibonacci Index

The Fibonacci index of a graph is the number of its stable sets. This parameter is widely studied and has applications in chemical graph theory. In this paper, we establish tight upper bounds for the Fibonacci index in terms of the stability number and the order of general graphs and connected graphs. Tur\'an graphs frequently appear in extremal graph theory. We show that Tur\'an graphs and a connected variant of them are also extremal for these particular problems.Comment: 11 pages, 3 figure